This invention relates generally to improvements in irrigation sprinklers of the so-called micro-stream type having a rotatably driven vaned deflector for sweeping a plurality of relatively small water streams over a surrounding terrain area to irrigate adjacent vegetation. More specifically, this invention relates to an improved rotating stream sprinkler having a ball drive rotor for rotatably driving the deflector in a succession of relatively small angular increments or steps, in combination with a speed control brake for maintaining the rotational speed of the vaned deflector substantially constant throughout a range of normal operating pressures and flow rates.
Rotating stream sprinklers, sometimes referred to as micro-stream sprinklers, are well known in the art of the type for producing a plurality of relatively small outwardly projected water streams swept over surrounding terrain. In one common form, one or more jets of water are directed upwardly against a rotatable vaned deflector which has a vaned lower surface defining an array of relatively small flow channels extending upwardly and turning radially outwardly with a spiral component of direction. The water jet or jets impinge upon this underside vaned deflector surface to fill these curved flow channels and to rotatably drive the deflector. At the same time, the water is guided by the curved flow channels for projection generally radially outwardly from the sprinkler in the form of a plurality of relatively small water streams to irrigate adjacent vegetation. As the deflector is rotatably driven, these water streams are swept over the surrounding terrain area, with a range of throw depending in part on the channel configuration. Such rotating stream sprinklers have been designed for irrigating a surrounding terrain area of predetermined pattern, such as a full circle, half-circle, or quarter-circle pattern. For examples of such rotating stream  sprinklers, see U.S. Pat. Nos. 4,660,766; 4,796,811; 4,815,662; 4,971,250; 4,986,474; Re. 33,823; 5,288,022; 5,058,806; 5,845,849; and 6,244,521.
In rotating stream sprinklers of this general type, it is desirable to control or regulate the rotational speed of the vaned deflector and thereby also regulate the speed at which the water streams are swept over the surrounding terrain area. In this regard, in the absence of speed control or brake means, the vaned deflector can be rotatably driven at an excessive speed up to and exceeding 1,000 rpm, resulting in rapid sprinkler wear and distorted water stream delivery patterns. A relatively slow deflector rotational speed on the order of about 4–20 rpm is desired to achieve extended sprinkler service life while producing uniform and consistent water stream delivery patterns. Toward this end, a variety of fluid brake devices have been developed wherein a rotor element carried by the vaned deflector is rotatably driven within a closed chamber containing a viscous fluid. In such designs, the viscous fluid applies a substantial drag to rotor element rotation which significantly reduces the rotational speed of the vaned deflector during sprinkler operation.
While such fluid brake devices are effective to prevent deflector rotation at excessive speeds, the actual rotational speed of the deflector inherently and significantly varies as a function of changes in water pressure and flow rate through the sprinkler. Unfortunately, these parameters can vary during any given period or cycle of sprinkler operation, resulting in corresponding variations in the water stream delivery patterns for irrigating the surrounding vegetation. In addition, such fluid brake concepts require the use and effective sealed containment of a viscous fluid such as a silicon-based oil or the like, which undesirably increases the overall complexity and cost of the irrigation sprinkler.
Copending U.S. Ser. No. 10/310,584, filed Dec. 4, 2002, discloses an improved rotating stream sprinkler having a nonfluid speed control brake for maintaining the rotational speed of the vaned deflector substantially constant throughout a range of normal operating pressures and flow rates. A resilient brake pad is mounted between a friction plate rotatable  with the deflector and a nonrotating brake disk, with one or more of these components incorporating a suitably tapered contact surface designed for varying the frictional resistance to deflector rotation in a manner achieving substantially constant rotational speed during normal operating conditions. While this improved sprinkler design beneficially avoids the problems and disadvantages associated with prior fluid brake concepts, the deflector is continuously rotated to sweep the water streams over the surrounding terrain to be irrigated. Such continuous rotation of the deflector inherently reduces the range of throw of the outwardly projected water streams.
There exists, therefore, a need for further improvements in and to rotating stream sprinklers of the type for sweeping a plurality of relatively small water streams over a surrounding terrain area, particularly with respect to maximizing the range of the outwardly projected water streams while at the same time maintaining the rotational speed of a vaned deflector at a controlled, relatively slow, and substantially constant rate. The present invention fulfills these needs and provides further related advantages.